The excitation mechanism of solar five-minute oscillations is studied in this pa- per.We calculated the non-adiabatic oscillations of low-and intermediate-degree(l = 1-25) g4-p39 modes for the Sun.Both the thermodynamic and dynamic couplings are taken into account by using our non-local and time-dependent theory of convection.The results show that all the low-frequency f-and p-modes with periods P>5.4 minutes are pulsationally un- stable,while the coupling between convection and oscillations is neglected...